One of the best aspects of Marvel's Agents of S.H.I.E.L.D. is that the series is structured much like the comic books it's based on. Each season follows an "event" storyline that builds up into the ones that follow. The result is a series that brings the fans back season after season to see what's going to happen next, which popular characters from the comics will make an appearance, and how closely the series relates to the books.
Marvel's Agents of S.H.I.E.L.D.'s story arcs are called pods, and most seasons have one large one while others have two to three. Pods have been described as "7-10 episodes [that feature] little 'enclosed plotlines' that formed a larger whole." This structure will continue as the show enters its sixth and seventh seasons. Each pod has its fans, but some are considered significantly better than others.
What Happens: In the final two episodes of the fourth season, the team must find and deal with Aida, but there's a catch. She has found a way to make herself an Inhuman body in the real world, filled with the various powers she took from others within the Framework. As a result, catching and stopping her isn't as easy as it was previously. This arc also sees the end of the Framework.
Coolest/Most Bad-Ass Moment: When the Framework comes to an end for Radcliffe and he utters the line, "This is the way the world ends. Not with a bang, but a..."
What It Sets Up: The end of the fourth season establishes the events that build into "Lost in Space."
What Happens: "Agents of HYDRA" is the third and final pod from the fourth season. With the main characters stuck in Aida's framework, life looks rather different. S.H.I.E.L.D. has fallen while HYDRA has taken its place, and the woman in charge is none other than Aida, otherwise known as Lady Hydra within the Framework. At her side is Fitz, whose father is still around to lead him down a path of darkness as Aida's righthand man.
Coolest/Most Bad-Ass Moment: When the team finally escapes in a massive fight at the very end.
What It Sets Up: The inevitable confrontation with Aida in the real world. However, things aren't as simple as they used to be thanks to the Darkhold...
What Happens: The opening episodes of the series don't form a structured pod like the rest, but they do establish what follows. In the first 13 episodes, the series establishes the main characters and begins to explain how Agent Phil Coulson was returned to life after his encounter with Loki in The Avengers. Skye is also introduced, and her inclusion on the team is developed, as well.
Coolest/Most Bad-Ass Moment: When Coulson's resurrection is finally revealed and the nature of Tahiti (it's a magical place) comes to light, it makes for an incredibly compelling scene.
What It Sets Up: The first 13 episodes establish the presence of Clairvoyant, a mysterious threat who will be revealed in "Uprising."
What Happens: "Ghost Rider" is the first of three pods in the fourth season. It serves as the introduction of Robbie Reyes' Ghost Rider. It takes a few episodes, but when "The Good Samaritan" hits, the truth of his origin is revealed! When the action ramps up towards the pod's conclusion, the Agents of S.H.I.E.L.D. must team up with the Ghost Rider against a common foe.
Coolest/Most Bad-Ass Moment: When Ghost Rider finally gets his vengeance and takes several bad guys out with his flaming chains.
What It Sets Up: "Ghost Rider" merges into and sets up the second pod in the season, "LMD," which focuses on the proliferation of Life-Model Decoys in the MCU.